Members of the Bunyaviridae family are among the most widespread viruses in the world. genus Phlebovirus family Bunyaviridae, is a mosquito-borne-virus whose cyclic epidemics have had devastating economic effects on livestock populations throughout much of sub-Saharan Africa. In humans, RVFV infection causes inflammation of the brain, spinal cord, and meninges, retinitis with visual impairments, and liver necrosis with hemorrhaging. Due to its increasing susceptibility, spread, vector plasticity, and ease of aerosolization, RVFV has been listed as an emerging infectious disease and a category A select agent by the CDC. Despite being recognized as an emerging threat, relatively little is known about the virulence mechanisms of RVFV and there are currently no FDA licensed vaccines or therapeutics for RVFV. The long-term goal of our research is to develop a greater understanding of the interplay between viral and cellular proteins in order to elucidate the fundamental mechanisms of host susceptibility to viral infection and disease. By identifying these mechanisms we hope to develop therapeutics targeted to the host, establishing a much broader range of targets with decreased likelihood of viral adaptation. Our preliminary data indicate that RVFV infection induced phosphorylation of a number of DNA damage signaling proteins including, ATM (Ser1981), Chk.2 (Thr68), Histone H2AX (Ser139) and p53 (Ser15). The induction of these pathways does not appear to be dependent on increased DNA damage, but rather due to the viral protein NSs. A detailed analysis of p53 phosphorylation events revealed that p53 was highly phosphorylated on multiple N-terminal residues and the protein stabilized. These phosphorylation events were also dependent on NSs. In addition, NSs dependent S phase arrest was observed following RVFV infection, which can be reversed by treatment with ATM and Chk.2 inhibitors. Noxa, a p53 regulated pro-apoptotic gene, was significantly upregulated following RVFV infection. Likewise, RVFV infection of p53 wildtype cells resulted in greater viral induced cell death as compared to p53 null cells. Furthermore, loss of p53 results in 100 fold decreased viral replication, suggesting that the induction of these pathways and the resultant S phase arrest are important for viral replication. Collectively our data led us to our central hypothesis that DNA damage signaling cascades are being activated and potentially exploited following RVFV infection, directly impacting viral replication. Recent findings by Dr. Cherry's group indicate that fatty acid synthesis is important for RVFV RNA synthesis. As fatty acid synthesis is increased during the S phase, these findings provide a novel link between fatty acid biosynthesis, S phase arrest and RVFV RNA synthesis. The short-term goal of our research is to determine the mechanism by which RVFV NSs induces DNA damage signaling and how this signaling aids in viral replication in vitro and in vivo. We will accomplish this goal through the following specific aims: 1) Determine the mechanism by which NSs induces DNA damage signaling and its importance to viral replication in vitro and 2) Determine the importance of RVFV induced DNA damage signaling in vivo.